How do you write the first five terms of the geometric sequence #a_n = 5a_(n-1)#; #a_1 = 3#?

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Answer 1 · 2016-01-19T13:55:38

#3, 15, 75, 375, 1875#

#a_n = a_1r^(n - 1)#

#a_n = 5a_(n - 1)#

#a_1 = 3#

#a_2 = 3r#

But
#a_2 = 5a_(2 - 1) = 5a_1#

#=> 3r = 5a_1#
#=> 3r = 5*3#
#=> r = 5#

Using #a_n = a_1r^(n - 1)# with #a_1 = 3# and #r = 5#, the first 5 terms are

#3, 15, 75, 375, 1875#